“Who gave us the sponge to wipe away the entire horizon? What were we doing when we unchained this earth from its sun?” cries Nietzsche’s madman in a famous parable of The Gay Science. “Are we not continually falling? Aren’t we straying as though through an infinite nothing [5, 7]? Isn’t empty space breathing at us

Boundary is such a common-sense concept that it hardly needs to be glossed. Indeed, the definition of the word in the Oxford English Dictionary flirts with tautology in its obviousness: “that which serves to indicate the bounds or limits of anything….” …